Metallurgy of zinc.



A. L. J. QUENEAU. METALLURGY 0F ZINC.

nrucngon FILED APR. 1, 1909.

Patented June 17,1913.

3 SHEETS-SHEET 2.

I VENTOR ATTORNEYS UNITED STATES PATENT OFFICE.

AUGUSTIN LEON JEAN QUENEAU, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOB TOQUENEAU ELECTRIC ZINC FURNACE COMPANY, OF PHILADELPHIA, PENNSYL- VANIA,A CORPORATION OF DELAWARE.

KETALLUBGY OF ZINC.

Specification of Letters Patent.

Patented June 1'7, 1913.

Application filed April 7, 1909. Serial No. 488,399.

sylvania, have invented certain new and useful Improvements in theMetallurgy of Zinc; and I do hereby declare the following to be a full,clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

The standard practice of today in the smelting of zinc ores is to roastthe ores to remove the sulfur from the sulfid ores or the carbon dioxidfrom the carbonates. The resulting zinc oxid mixed with finely dividedcoal is reduced in small fire clay rctorts (holding from 50 to 150pounds of charge) fitted up in tiers within a heated furnace, the heatpassing through the wall of the ret-orts. The zinc vapors issue intoshort fire clay receivers where they condense into molten metal. Thatthis process is an extremely inetlicient one has long been recognized,but the many attempts to supplant it have heretofore been unsuccessful.The inetficiency of the process arises from the fact that the oremixture must be heated to about 1200 degrees C. Consequently, theretorts must have thin walls, in order to transmit to the charge theheat required, and must be made of fire clay which alone possesses thenecessary plasticity for the purpose. The fire clay retorts areditlicult to make, fragile, readily attacked by slag, and absorbconsiderable quantities of zinc, which is lost when the retorts aredestroyed. The heat efficiency is very low and the average life of theretorts hardly more than thirty days. The condensation of the zinc vaporalso presents ditli'culties, and much of it is collected as a metallicpowder which must be re-distilled in order to be condensed to the liquidstate.

In contrast to the standard practice above indicated, the presentinvention permits the treatment of the ores in receptacles of largesize, adapted to contain a correspondingly large charge. Furthermore, itpermits the thickness of the walls of the containing vessel to begreatly increased and permits them to be made of a material moreresistant to the action of slag than fire clay. Moreover, in thetreatment of zinc ores containing sulfur it is not necessary, in orderto adapt them to the uses of the invention, that they should first bebrought to a sweet roast, inasmuch as the reduction of the ores by meansof 1ron, or by means of lime and carbon, according to the formulae canbe readily effected, particularly in view of the fact that during thereducing operation, the reducing agents are brought into intimatecontact with the ore. It is, therefore, desirable merely to roast thezinc sulfid ores to a sulfur content of five or six per cent, which canbe brought about with a small expenditure of coal, and, in fact, zincores in the new or unroasted condition may be treated in accordance withthe invention. Furthermore, in the practice of the invention, zinc orescarrying copper, lead, iron, gold or silver can be commercially treated,and to particular advantage if to the zinc ores carrying gold or silver,some copper ore is added to form a copper matte to take up the preciousmetals.

In the prevailing practice, the employment of ores high in slag-formingelements corrosive to the fire clay walls of the retorts is avoided, asit is necessary to have the reduction residues present ina drypulverulent condition in order to allow of their easy removal from theretorts, and for this reason a large excess of reducing material is usedto act as a sponge, holding apart any slagforining material. In thepresent invention, on the other hand, as will appear from thedescription of the furnace, it is necessary to .have the residualproducts of the treated charge in a highly fluid state and of a.chemical composition having the minimum dissolving power for zinccompounds. It follows, therefore, that ores that are of an objectionablechemical composition for the prevailing ractice but which are of lowcost are higlily desirable for the practice of the present invention. Inthe practice of the present invention it is also feasible to preheat theore to a high temperature before admitting it into the reductionfurnace, for

and

instance, to pre-heat it to a temperature of say 1000 C. Thispre-heating of the ore may be attained in the ordinary roasting kilns,and is incident to the roasting of the ores in such kilns; so that theore, after its sulfur content is reduced to the low limit incident tothe roasting operation, and is discharged from the kiln, may bedischarged directly into the zinc-reducing furnace, or may betemporarily stored in a receptacle which will conserve or substantiallyconserve the high heat of the ore until the zincreducing furnace isready to receive it. Whether the high preliminary heat of the ore is anincident of the roasting operation or is otherwise imparted to it, suchtemperature is higher than the temperature at which the coal or otherreducing agent would burn in the air. For this reason, the mixin of thereducing agent with the ore shoulf preferably take place within thefurnace itself. Nevertheless, it will be found of advantage to alsopre-heat the reducing agent, but at a temperature lower than that atwhich it would burn in the air, the ore and the reducing agent beingcharged separately into the reducing furnace and mixed therein byrevolving the latter. I

In carrying out the invention, it will be desirable to heat the interiorof the rotatory reduction furnace to a high temperature, referably bythe electric current) before admitting the furnace charge. To thenmaintain the reducing temperature during the subsequent reduction of theore and distillation of the zinc therefrom a molten fluid resistor isemployed, which is introduced into the furnace chamber, in such manneras to form a path for an electric current of such a character as tomaintain the'fluidity of the resistor and the high temperature necessaryto carry on and complete the reducing op eration, the surfaces ofcontact between the char 0 and the fluid resistor being constanl yrenewed b reason of the rotative movement of the mace chamber, therebyincreasing the speed of the reaction. The

zinc vapors given oil by the charge are received in condensers of suchconstruction and arrangement that the vapors are condensed therein tothe metallic liquid state.

In the accompanying drawings, Figure 1 represents a longitudinal centralsection, partly in elevation, of a furnace and its condensers ada tedfor the practice of the invention. Fig. 2 represents a section thereoftaken on a lane indicated by the line 22 of F i 1. Eig. 3 represents, anend view of the fl irnace, with the corresponding condenser removed.Figs. 4 and 5 re resent central longitudinal sectional views s owingmodifications of the furnace structure.

Referring to the drawings, it will be noted that the furnace, which isof the'rotary type, is provided with a shell 10, preferably of lowcarbon steel, lined interiorly with refractory material of suitablephysical characteristics. In the modification shown in Figs. 1, 2 and 3,the outer blocks a proximate to the steel shell, are of ood heatinsulating fire brick, whereas the inner blocks b are preferably ofchrome bricks, inert to slags and zinc vapors.

The metal shell of the furnace as illustrated in the drawings, ispreferably cylindrical in shape, and is supported upon bands or tires(1, resting on rollers c, the axis of the furnace being preferablyhorizontal.

The shell is also provided with a band gear driven through theintermediacy of a gear 9, which constitutes an element of a variablespeed drive, adapted to be actuated from a variable speed electricmotor, so that the number of revolutions per minute of the furnace maybe readily varied.

Each end of the furnace is faced with an annular metallic plate h,preferably of low carbon steel or other like appropriate conductingmetal, which plate is provided with an annular series of apertures nearits outer edge or border, through which apertures pass a correspondingseries of headed bolts 5, which bolts likewise pass through the rings j,l, and are provided at their inner ends with screw-threads havingadjusting and locking nuts, as shown. Springs m are interposed betweenthe rings j and l and encompass the shanks of the bolts, so that bymeans of the said nuts, the plates 71 may have a capacity forindependent movement, to correspond to the efiects'of heat expansion inthe furnace, but will. nevertheless be held in strong elastic,adjustable contact with the furnace ends. The bolts i are held out ofelectrical contact with the plates and rings through which they pass bymeans of insulating sleeves, as shown, and the'springs m rest againstthe ends of these sleeves and are out of electrical contact with therings 7', I, so that no electric current shall pass through the springsto affect their temper or resiliency.

The end lining of the furnace is made up of a circular course ofgraphite blocks 1:, makin good electric contact with each other, and aso of courses of fire brick and chrome bricks r. A casting s, insulatefrom the late It serves to sustain by suitable brac ets the condenser A(one on each end of the furnace), which condenser and its prolong Brevolve with the furnace struc ture and communicate with ,the interiorthereof by means of the refractory connection 9. Between the plate h andthe end lining of the furnace may be interposed any suitable packing,for instance, asbestos, as indicated at w. The non-condensable gasesescaping from the prolongs B may conveniently be led away throughsuitable stacks C, and the prolongs themselves may be provided withinterior partitions v to lessen the liability of small explosionstherein.

The plates 11 are provided with an annular recess or depression :12,which makes reliable electric contact with the outer ends of the coursesof carbon blocks a at the two ends of the furnace, and these depressedportions :10 are held in such contact, b means of the springs m. At oneend of tie furnace, the depressed portion 00 forms a path for a carbonor metallic brush y constituting one of the terminals of an electriccircuit, so that, durin the revolution of the furnace, the electriccurrent will be transmitted with certainty to that end of the furnaceand to the circular course of carbon bricks, whatever longitudinalexpansion ma y take place. The other carbon or metallic brush 2constituting the opposite terminal of the current employed makes contactwith the metallic shell a of the furnace. The ring at said opposite endis in electric contact with the shell (1 and is likewise in electriccontact with the corresponding plate h, through the intermediacy of thespring metal plates 0.

In all three modifications of the furnace illustrated in the drawings,the arrangement of parts, hereinbefore specifically described, ispreserved. In the modification shown in Figs. 1 and 2, however, theinner lining of chrome bricks I) occupies substantially the entirelength of the furnace, opening at its ends against the courses of carbonblocks a. In the modification shown in Fig. 4, the lining of'chromebricks b is not continuous, but is interrupted by intermediate sectionallinings of of graphite blocks. Finally, in the modification shown inFig. 5, the inner lining is made up of chrome bricks or blocks andgraphite bricks or blocks arranged in a particular sequence, whosefunction will be hereinafter more fully set forth.

In all of the modifications, the metal plates h at one end of thefurnace are out of direct electric connection with the metal plates atthe other end of the furnace, and are intended to be electricallyconnected, during the operation of the furnace, through the intermediacyof a molten fluid resistor, which is adapted to extend longitudinally,either from end to end of the interior chamber of the furnace, or, so asto span any non-conducting areas that may exist therein. This fluidresistor is indicated by the letter D in Fig. 1, by D in Fig. 4, and byD in Fig. 5. It may consist of a metal, a'salt, or a slag, adapted tomaintain fluidity during the assage of an electric current of suitablevo tage and amperage, which current ma: either be direct or alternating.

In most instances, I prefer to emplov cast iron as the material of themolten fluid resistor, and. to give it such a chemical composition as toobtain not only high specific electric resistance, but also highfluidity at relatively low temperatures, say about 1200 C. Such an alloymay be obtained, for instance, by adding various proportions ofphosphorus, nickel and chromium to cast iron, the proportions of themetallic elements being such as to form an alloy of iron, phosphorus,nickel, chromium and carbon of the minimum melting temperature, that isto say, the minimum eutectic for these five elements. The percentage ofcarbon present in solution in the alloy is automatically regulated bythe equilibrimn law of solution for a given temperature, there beingalways present an available excess of readily soluble carbon. Theelements phosphorus, nickel and chromium are recommended because theyhave the property of giving high electrical resistance, while phosphorusgives high fluidity, and because these elements have a lower chemicalafiinity for sulfur than has iron. There is always present in the zincore charge a large excess of iron to always satisfy whatever sulfur hasremained in the roasted zinc ore. It follows, therefore, that thequantities of phosphorus, nickel and chromium originally present in themolten cast iron resistor, will be practically maintained constant, excet for the mechanical losses, such as metal ic shot, entrapped by theslag or mat-tes. It will be, of course, apparent that the advantage ofhigh fluidity of the molten resistor is to permit it to quickly adjustits level during the rotation of the furnace, and that the advantage ofhigh specific electrical resistance is that, for the depth of resistornecessary, a high electrical efficiency is nevertheless secured, 0.,that the ratio of the ohmic resistance of the molten resistor to thetotal of the electrical resistances between the molten resistor and thebrushes is at a maximum.

In the modification shown in Fig. 4, the molten fluid resistor isillustrated as brid ing portions of the inner lining, in SllCl mannerthat the passage of the electric current will take place in part throughmolten resistor and in part through solid resistor. The number ofbridges of molten resistor l) and of intervening solid resistor ofgraphite n may vary in accordance with the particular thermal effectsdesired. Thus, in Fig. 4, there are shownthree bridges I) of moltenresistor andtwo intervening lining sections n of raphite resistor, but Ido not confine myself to this particular number, as it is evident thatone ormore of the bridges may be suppressed and their places substitutedby graphite resistor, or that their number may be increased, if desired.

In the modification shown in Fig. 5, the

that is, consisting in part of a molten resister and of a solid graphiteresistor, so as to correspondingly increase the resistance within thefurnace and obtain higher heating effects. In this instance, I haveshown a single bridge of molten resistor D occupying a position midwayof the furnace lining, but it, is, of course, evident that this bridgemay be supplemented by others, as in the instance illustrated in Fig. 4.A particular feature of the arrangement shown in Fig. 5 is that in orderto permit uniform lineal: expansion throughout all of the longitudinalrows of the interior lining, I have so disposed the bricks or blocksthat in each longitudinal row there will be the same number of bricks orblocks, although each row is made up in part of chrome bricks and in"part of graphite bricks. In this Fig. 5, the chrome bricks areindicated by the white rectangles and the graphite bricks by the blackones, and it will be noted that the graphite bricks of one longitudinalcourse overlap the graphite bricks of the courses on each side thereof.It, therefore, results that there is continuity of electricalconnection, in a zigzag or oblique line from each annular course ofgraphite bricks n at the ends of the furnace to the middle Well occupiedby the molten resistor, and furthermore, that each of the longitudinalcourses is made up of the same number of chrome bricks or graphite briks; for instance, in the example shown in Fig. 5, each longitudinalcourse of the internal lining is made up of fifteen (15) graphite bricksor blocks and eighteen (18) chrome bricks or blocks (including the threechrome bricks at the central well or bridge) and itwill be equallyapparent that this arrangement provides'an equal coefficient ofexpansion for all of the longitudinal courses.

Condensation of the zinc vapor to the liquid condition will take placein the zinc chamber or chambers A, which rotate with the furnace, andthese condensers may be cooled, in addition to the cooling which theyexperience from rotatin in the open air, by a jet or jets of air,lrected upon them. Any condensable matter carried off from thecondensers A into the prolong B are recovered therein and theproductions of combustion are collected and carried off through thestack or stacks C.

In the practice of the invention, the furnace may be charged in anysuitable manner, either by removing one or the other of the condensers,or by admitting the charge through an aperture in the shell and lining,which aperture is normally closed by a plug E (see Fig. 2) and theremovable brick sections thereunder. Before admittin the charge,however, the furnace is heate preliminarily. This heating is effectedeither by a gas or oil flame, but preferably by admitting into thefurnace, a body of molten lead, or other metal of low melting point,

and passing the electric current through the furnace, while subjectingit to a slow movement of rotation. When the furnace lining has attainedthe necessary temperature, the furnace is stopped and the lead or otherlike metal is tapped off. A known amount of resistor, referably meltedbefore it is inserted in tlie furnace, is then introduced, suflicient toreach the level desired. The furnace is then charged, preferabl withroasted ore direct from the roasting urnace, and at the high temperatureincident to such roasting, and also with the necessary amount of carbon,also preferably pre-heated. The furnace is then again set in rotation,and the reducing and condensing operation proceeds, the electricalcurrent maintaining the necessary thermal conditions. When the reductionof the charge is completed, the contents of the furnace may be tapped,throu h the same aperture that had served or charging it, it beingunderstood that the capacity of the furnace to rotate permits the slagto be tapped off separately from the metal remaining in the furnace. Ithas already been indicated that where the zinc ores treated contain anyof the precious metals, it will be desirable to add enough copper ore tothe charge to form a copper matte, to insure their recovery.

Speaking further of the general operation of the invention, it will benoted that the agitation of the contents of the furnace, due to therotation, results in close and intimate contact -between theconstituents of the furnace charge, thereby shortening the time requiredfor the complete chemical action, and not only increasing the dailyfurnace capacity, but also increasing the heat efficiency of thefurnace, as heat is radiated, for a given char e, durin a shorter spaceof time, so that t e loss 0 radiated heat is correspondingly less.Furthermore, the rotation and agitation of the contents of the furnaceresult in the rapid attainment of an equilibrium of temperaturethroughout the mass of the charge, and the rotation of the furnace, byconstantly renewing the surface of the lining in contact with the heatinmedium, keeps the whole furnace at a big heat. Evident] however, theupper part of the furnace wil be at all times to some extent cooler thanthe lower part which contains the molten resistor. This is a desirablefeature, in that it keeps at aminimum the temperature of the issuinggases and vapors, thus facilitating the condensation of the latter whilekeeping at a minimum the number of heat units carried away by the uses.

at I claim is:--- 1. An electric furnace, having an interior lining madeup of longitudinal courses consisting of the same number of conductingand non-conducti blocks, so as to equalize expansion, the coii iuctingblocks of the adjacent courses overlapping so as to conduct the electriccurrent from one to the other.

2. An electric furnace, having a rotatory main body chamber, providedwith an interior peripheral lining having a series of longitudinalcourses of solid peripheral conductors forming a part of said lining andseparated from each other by longitudinal courses of solid peripheralnon-conductors, said conductors having a break in their electricconductivity and being bridged successively at the bottom of the chamberand acrosls said break by molten resisting materia 3. An electricfurnace, having a rotatory main body chamber, provided with an interiorperipheral lining, having solid peripheral conductors forming a part ofsaid- AUGUSTIN LEON JEAN QUENEAU.

Witnesses:

JOHN C. PENNIE, LAURA B. PENFIELD.

